Why use a Lens filter?
Lens filters are used to control/attenuate parts of the spectrum (colours of light) before they enter the lens/camera. This can be in the UV (low end), visible (mid range) or NIR (high end) of CCD/CMOS camera sensitivity.
There are an almost infinite number of different filters. They are usually described as low-pass, high-pass or band-pass. The full description of a filter specifies a particular wavelength of light (the cut-off point or band centre) followed by low-pass, high-pass or band-pass.
The cut-off or centre wavelength is never absolute. All filters have what is called a ‘roll-off’ characteristic that is usually available graphically. This describes how accurately the filter is eliminating or passing unwanted light. Generally, the steeper the roll-off, the higher the quality of the filter
Midwest Optical Lens Filters Range:
Midwest Optical Systems (MidOpt) is the worlds leading resource for off-the-shelf and custom machine vision filters, lenses and accessories used in industrial imaging applications. Security, surveillance, scientific, medical and other markets are also served.
BANDPASS FILTERS: MidOpt Bandpass Filters are the simplest, quickest and most cost-effective way to improve the image contrast, repeatability, and long term stability of any industrial vision system.
- BP Series:For standard machine vision and surveillance applications
- BN Series: For outdoor applications or situations involving overwhelming ambient light
- BI Series: For laser diode or other narrow spectrum light source applications
DUAL BANDPASS FILTERS: For Day/Night Color Camera Applications are ideal for applications that use a color camera during the day and IR illumination at night – ensuring that clear, accurate images are acquired under all lighting conditions.
LONGPASS FILTERS: Longpass filters let longer visible and/or infrared wavelengths pass while blocking shorter wavelengths of light. Mainly for use in monochrome (black and white) imaging applications, they can help to improve contrast, resolution and separate colors while maximizing brightness of surroundings in the vicinity of the subject under inspection or surveillance.
SHORTPASS FILTERS: Shortpass filters are useful for improving contrast, resolution and separating colors in black and white or color applications.
SP Series – VIS Pass
- Designed to have a sharp transition between shorter wavelengths (which are passed) and longer wavelengths (which are blocked).
- Improve contrast and resolution
- Separate colors in black/white or color applications
SP Series – NIR Block/VIS Pass
- Block IR light for accurate color rendition in digital cameras
- Commonly placed over the cameras image sensor
POLARING FILTERS: Polarizing filters reduce unwanted reflection or specular glare and can also be used to check stress patterns in transparent glass and plastic.
For smooth surfaces or surfaces covered with grease, oil, or liquid, achieve the best results by using a polarizing filter over the lens in conjunction with polarizing film or polarizing glass sheet over the light source. Most polarizers are wavelength range specific; visible or infrared polarizing filters or filter sheet materials are offered.
NEUTRAL DENSITY FILTERS: Light used to image any nonmetallic surface will produce polarized light in reflection, therefore the use of linear polarizers can often result in appreciable benefit in industrial imaging applications.
Sunglasses for your system, ND filters reduce light intensity without affecting apparent color. They also allow for longer exposure times and reduced depth of field by using a wider iris opening, thus improving the separation of subject matter from background information.
ND Series – VIS, Absorptive
- Reduce light intensity in the visible spectrum without affecting color and contrast
- Used with a monochrome or color camera working in the visible (VIS) spectrum
- Eliminate over-saturated images. ND filters transmit and block in the near infrared as well the visible spectrum, however specific neutrality is not controlled in the infrared.
Ni Series – VIS/NIR, Low-Reflectivity
- Reduce light intensity neutrally throughout the VIS and NIR spectrums
- Use with monochrome or colour cameras, or can be placed over bright light sources
- Made with low-expansion, heat-resistant Borofloat glass, Ni filters can be used to aid in thermal load reduction
- Superior parallelism and surface quality
PROTECTIVE FILTERS: Available in glass or acrylic substrates, protective filters shield lenses and lighting from impact, dust and harsh environments – while blocking shorter UV wavelengths.
- Glass substrates with tight control of parallelism and cosmetic surface quality
- Block UV while passing visible and near-IR wavelengths
- Spectrally neutral within the designated passband
- Economical solution for covering lighting and camera enclosures
- Available in 1-2 days in complex shapes and configurations
- Useful for: indoor and outdoor applications; can be used in conjunction with existing glass covers
LIGHT BALANCING FILTERS: Corrects apparent color and contrast introduced by artificial white lighting, restoring natural colors.
Used to modify the color balance in LED, fluorescent, halogen, metal halide, tungsten, and other white lighting, making colors appear more natural. The LA series (Minus Blue) reduce blue shading that often strongly predominates in white LED and xenon strobe lighting. The LB series (Minus Red) reduces the red hue found with some tungsten and halogen lighting.